Centering device, in particular for a probe measuring device

ABSTRACT

A centering device, in particular for a tracer-type measuring instrument ( 1 ), is proposed. The centering device comprises an instrument carrier ( 3 ) defining an instrument axis ( 7 ), a carrying shank ( 41 ) defining a shank axis ( 43 ) and a centering holder ( 45 ) holding the instrument carrier ( 3 ), with the instrument axis ( 7 ) parallel to the shank axis ( 43 ), radially movably to the latter, but so as to be capable of being fixed to the carrying shank ( 41 ). The centering holder ( 45 ) is designed as a parallelogram guide with a parallelogram-link region ( 59 ), or a plurality of these regions, distributed about the shank axis ( 43 ) and the instrument axis ( 47 ) and extending along these axes ( 7, 43 ). Such a parallelogram guide may be integrally formed in one piece on the carrying shank ( 41 ) and/or on the instrument carrier ( 3 ), thus reducing the outlay in terms of production. Setscrews ( 69 ) distributed on the circumference of the parallelogram guide make it possible to adjust the shank axis ( 43 ) in relation to the instrument axis ( 7 ).

The invention relates to a centering device, in particular for atracer-type measuring instrument.

For example, the German laid-open publications DE-A-41 00 323, DE-A-19502 840 and DE-A-100 14 630 disclose multicoordinate tracer-typemeasuring instruments, the tracing arm of which is displaceable in thedirection of a main coordinate axis defined by guides of a housing andcan be deflected transversely to this main coordinate axis by means of auniversal joint. The housing is held on a carrying shank, the shank axisof which runs coaxially to the main coordinate axis in the state of use.So that the main coordinate axis of the housing can be centered inrelation to the shank axis, the housing is provided, facing the carryingshank, with an axially perpendicular guide surface for the carryingshank and engages with a pin into a clearance of the carrying shank,said clearance allowing radial play between the carrying shank and thepin. The housing is consequently moveable axially parallel to thecarrying shank and can be centered with the aid of a plurality ofsetscrews held on the carrying shank and capable of being advancedtoward the pin. For fixing, an axial tension screw is provided, whichscrews the carrying shank to the housing. However, such a centeringdevice formed by the carrying shank of the housing necessitates acomparatively high outlay in production terms, particularly because ofthe guide surfaces and locking means used there.

The object of the invention is to specify a centering device which issuitable, in particular, for a tracer-type measuring instrument andwhich can be produced more simply than hitherto.

The invention proceeds from a centering device, in particular for atracer-type measuring instrument, which comprises:

-   An instrument carrier defining an instrument axis,-   A carrying shank defining a shank axis,-   A centering holder holding the instrument carrier, with the    instrument axis parallel to the shank axis, moveably radially in    relation to the latter, but so as to be capable of being fixed to    the carrying shank,-   and is characterized in that the centering holder is designed as a    parallelogram guide with a parallelogram-link region distributed    about the shank axis and the instrument axis and extending along    these axes.

Such a centering holder manages without axially perpendicular guidesurfaces and can therefore be produced substantially more simply andtherefore more cost-effectively than in the case of conventionalcentering devices. Even though the centering device according to theinvention is preferably used in a tracer-type measuring instrument, suchas are described, for example, in the German laid-open publicationsDE-A-41 00 323, DE-A-195 02 840 or DE-A-100 14 630, such a centeringdevice can also be employed advantageously in other fields of use. Forexample, the centering device may be an integral part of a tool holderwhich holds a rotary tool, such as, for example, a drill, milling cutteror the like, centrically to the axis of rotation of the spindle of amachine tool. This applies particularly to those tool holders which holdthe rotary tool in a manner in which the latter is shrunk into a sleeveportion thermally expandable, for example, by means of inductiveheating. Such tool holders have, for connection to the machine toolspindle, a standard coupling, for example in the form of a steep-angletaper or the like. In this case, the centering device according to theinvention is arranged in the force transmission path between thestandard coupling of the tool holder and the sleeve portion holding therotary tool. In such a case, the carrying shank of the centering deviceaccording to the invention is designed as a standard coupling and theinstrument carrier as a sleeve portion.

The parallelogram-link regions may be a multiplicity of links, forexample in the form of bars, which are separate from one another and arearranged about the carrying or instrument axis and which can bedeflected on all sides, especially when these parallelogram-link regionsare arranged in the manner of a segmented axially parallelcircular-cylindrical sleeve portion. However, an embodiment in which thesleeve portion is designed with a closed wall in the circumferentialdirection can be adjusted more accurately and can also be produced moresimply.

In a preferred embodiment, the centering holder has a connecting flangewhich surrounds the shank axis and the instrument axis and connects thecarrying shank to the instrument carrier and which has on its sidesfacing axially away from one another circular grooves which areconcentric to one another, overlap one another axially and delimit thesleeve portion radially between them. Such grooves can easily be workedinto the connecting flange and, by their axial depth and the radialdistance between them, determine the radial deflection properties of thesleeve portion. The annular regions of the connecting flange whichproject radially inward and radially outward beyond the grooves alsostiffen the centering holder, so that the parallelogram movement isessentially based solely on the deformation of the sleeve portion. Bothin embodiments in which the parallelogram-link regions are formed fromindividual bars and in embodiments with parallelogram-link regionsdesigned as a closed sleeve portion, there is preferably provision forthe at least one parallelogram-link region to be connected at its oneaxial end to a first annular portion of the centering holder and at itsother axial end to a second annular portion of the centering holder, andfor one of these annular portions to carry at least one, but preferablyat least three, setscrews which are distributed in the circumferentialdirection and are supported radially in the region of the other of theseannular portions. The common portions stiffen the axial ends of theparallelogram-link regions in relation to one another, the setscrewswhich are supported between the two annular portions ensuring a uniformdeflection of the link region. Expediently, the two annular portions arearranged coaxially one in the other, the outer annular portion carryingthe setscrews in a radially screwable manner. This makes it easier toadjust the setscrews.

The centering holder may be a component which is separate from thecarrying shank and from the housing. In a preferred variant whichsimplifies production, however, the parallelogram-link region isproduced with its axial ends integrally in one piece with a carryingshank and/or with the instrument carrier.

An exemplary embodiment of the invention is explained in more detailbelow with reference to a drawing in which:

FIG. 1 shows an axial longitudinal section through a tracer-typemeasuring instrument with a centering holder according to the invention,and

FIG. 2 shows an axial view of the centering holder.

The tracer-type measuring instrument, designated in general by 1 in FIG.1, comprises a housing 3, on which a tracing lever, designated ingeneral by 5, is guided displaceably in the direction of a measuringaxis 7 defined by the housing 3. Furthermore, the tracing lever 5 isguided on the housing 3, pivotably on all sides about a pivot point 11lying on the measuring axis 7, by means of a universal joint, here inthe form of a ball joint 9, and is prestressed resiliently by arestoring spring 13 into the position of rest illustrated in thedrawing, in a way which is also explained in more detail below. Thetracing lever 5 has a tracing arm 15 which projects out of the housingand of which the free tracing end 17 formed by a ball defines a tracingreference point 19 lying on the measuring axis 7 in the position of restof the tracing lever 5. In relation to the pivot point 11, a couplingarm 21 of the tracing lever 5 projects, opposite to the tracing arm 15,into a circular-cylindrical guide orifice 23 of the housing 3, saidguide orifice being centric to the measuring axis 7. An essentiallysleeve-shaped coupling piece 25 is guided in the guide orifice 23displaceably in the direction of the measuring axis 7 by means of aguide sleeve 27, for example a spherical guide bush of the typeexplained in DE-A-100 14 630. A digital path-measuring device 29 held onthe housing 3 detects the position of the coupling piece 25 in relationto the housing 3 by means of a digital path sensor 31 and indicates on adisplay 33 the value of the deflection in relation to the position ofrest, illustrated in FIG. 1, of the tracing lever 5. A mechanicallength-measuring dial gauge may also be provided instead of the digitalpath-measuring device 29.

The coupling piece 25 has, in the region of its end axially remote fromthe pivot point 11, an inner control surface 35 in the form of afrustoconical surface with a rectilinear generatrix, with which it bearsagainst a convex outer control surface 37, formed at the free end of thecoupling arm 21, of the tracing lever 5. The inner control surface 35 isrotationally symmetrical to the measuring axis 7, while the outercontrol surface 37 is rotationally symmetrical to the straight linethrough the tracing reference point 19 and the pivot point 11, saidstraight line coinciding with the measuring axis 7 in the position ofrest of the tracing lever 5. The outer control surface 37 has ageneratrix in the form of a segment of a circle. The restoring spring 13prestresses the coupling piece 25 in the direction of the tracing end 17and at the same time ensures a bearing contact pressure of the controlsurfaces 35, 37 bearing against one another.

During operation, the tracer-type measuring instrument 1 is held in amachine tool or a measuring instrument or the like by means of astandard coupling, for example a steep-angle taper shank, indicated at39, which is coaxial to the measuring axis 7. During an adjustingmovement of the tracing end 17 in the direction of the measuring axis 7which occurs during measuring operation, the coupling arm 21 drives thecoupling piece 25 which, in turn, adjusts the path-measuring device 29.During an adjusting movement of the tracing end 17 transversely to themeasuring axis 7, the coupling arm 21 pivots about the pivot point 11defined by the ball joint 9. The control surfaces 35, 37, which slide onone another along their generatrices during this pivoting movement ofthe coupling arm 21, convert the pivoting movement of the tracing lever5 to an axial movement of the sleeve-shaped coupling piece 25, in such away that the path-measuring device 29 measures the radial distancebetween the tracing reference point 19 and the measuring axis 7. Forfurther details of a tracer-type measuring instrument of this type,reference is made to DE-A-100 14 630.

The tracer-type measuring instrument 1 is provided with a carrying shank41, by means of which it can be clamped into the standard coupling 39 orinto another tool holder of the machine tool. For exact measurements, itis necessary that the measuring axis 7 defined by the housing 3 or thetracing lever 5 runs coaxially to a centric shank axis 43 defined by thecarrying shank 41. So that radial errors of alignment can becompensated, the housing 3 is held on the carrying shank 41 via acentering holder 45. The centering holder 45 allows axially paralleladjustment of the measuring axis 7 in relation to the shank axis 43. Forthis purpose, the centering holder 45 comprises a radially projectingconnecting flange 47 which is integrally formed in one piece on thecarrying shank 41 and which is screwed to an axially perpendicularfitting surface 49 with the aid of a plurality of axial screws 51. Theconnecting flange 47 forms, toward tracing end 17, a centering extension53, by means of which said connecting flange is guided with a closeradial fit in the guide orifice 23.

On sides located axially opposite one another, the connecting flange 47is provided with annular grooves 55, 57 which are concentric to theshank axis 43 and which overlap one another in the axial direction andbetween them delimit a circular-cylindrical axially parallel straightsleeve portion 59. An annular portion 61 formed by the bottom of theradially inner annular groove 55 connects that axial end of the sleeveportion 59 which faces away from the tracing end 17 to the carryingshank 41, while the axially other end of the sleeve portion 59 isconnected, by means of an annular portion formed by the bottom 63 of theouter annular groove 57, to the circumferential region 65 of theconnecting flange 47, said circumferential region being screwed to thehousing 3.

In at least three, here four, radial threaded holes 67 arrangeddistributed in the circumferential direction, are seated setscrews 69which are accessible radially from outside and which are supported withtheir inner ends, near the end facing axially away from the tracing end17, on the sleeve portion 59 and consequently, in the region of theannular portion 61, on the latter.

The sleeve portion 59 forms a parallelogram guide which can be deflectedon all sides transversely to the shank axis 43 and in which the sleeveportion 59 subjected to flexurally elastic stress forms a parallelogramlink deflectable on all sides. By the setscrews 69 being adjusted, thecarrying shank 41 is displaced parallel to the measuring axis 7, thesetscrews 69 at the same time assuming the function of operationalfixing. Since four setscrews 69 offset to one another in each case at90° are provided, the setscrews can be locked in pairs.

In the exemplary embodiment illustrated, the parallelogram guide isimplemented by an annularly closed sleeve extension. Instead of theannularly closed sleeve extension, a sleeve extension segmented in thecircumferential direction may also be provided, or else the sleeveextension is formed by a cage comprising axially running bars. In afurther variant, the connecting flange 47 may not only be connected inone piece to the carrying shank 41, but also to the housing 3. Inparticular, the last-mentioned variant is suitable for otherapplications of the centering holder 45, for example for applications inwhich the component corresponding to the housing 3 forms a sleeveportion for the shrink-fit holding of a tool shank of a rotary tool, asis customary in the case of toolholders which, for example, arethermally expandable inductively. The carrying shank may then bedesigned directly as a standard coupling similar to the standardcoupling 39.

1. A centering device, in particular for a tracer-type measuringinstrument, comprising: a) an instrument carrier defining an instrumentaxis; b) a carrying shank defining a shank axis; c) a centering holderholding the instrument carrier, with the instrument axis parallel to theshank axis, radially movably to the latter, but so as to be capable ofbeing fixed to the carrying shank, wherein the centering holder isdesigned as a parallelogram guide with a parallelogram-link region, or aplurality of these regions, distributed about the shank axis and theinstrument axis and extending along these axes.
 2. The centering deviceas claimed in claim 1, wherein the parallelogram-link region is formedby a circular-cylindrical sleeve portion axially parallel to the shankaxis and to the instrument axis.
 3. The centering device as claimed inclaim 2, wherein the sleeve portion is designed with a closed wall inthe circumferential direction.
 4. The centering device as claimed inclaim 2, wherein the centering holder comprises a connecting flangewhich surrounds the shank axis and the instrument axis and connects thecarrying shank to the instrument carrier and which has, on its sidesfacing axially away from one another, annular grooves which areconcentric to one another, overlap one another axially and delimit thesleeve portion radially between them.
 5. The centering device as claimedin claim 1, wherein the parallelogram-link region is connected at itsone axial end to a first annular portion of the centering holder and atits other axial end to a second annular portion of the centering holder,and in that one of these annular portions carries at least one setscrewwhich is supported radially in the region of the other of these annularportions.
 6. The centering device as claimed in claim 5, wherein oneannular portion carries at least three setscrews distributed in thecircumferential direction.
 7. The centering device as claimed in claim5, wherein the two annular portions are arranged coaxially one in theother, and the outer annular portion carries the at least one setscrewin a radially screwable manner.
 8. The centering device as claimed inclaim 1, wherein the parallelogram-link region is produced with itsaxial ends integrally in one piece with at least one of the carryingshank and the instrument carrier.